The present invention relates to a method of efficiently adsorbing and removing nitrogen oxides (NOx) which are contained in low concentrations in gases discharged by ventilation from various highway tunnels, mountain tunnels, underwater tunnels, underground roads, sheltered roads and the like (hereinafter referred to collectively as "highway tunnels").
Highway tunnels, especially those having a large length and a great vehicular traffic volume, must be ventilated at a considerable rate in order to assure the drivers and passengers of health and increase the least distance of distinct vision. Air is withdrawn also from tunnels of relatively short length for ventilation to control air pollution due to carbon monoxide (CO), NOx and the like which are concentrically released from the inlet and outlet of the tunnel when the tunnel is located in an urban or suburban area.
However, if the gas discharged by ventilation is released as it is in the neighborhood, the environment of the area concerned will not be improved. In particular, in the urban or suburban area where air pollution due to vehicular exhaust gases spreads along a plane, the dischaged gases could extend to form a highly polluted zone. Exactly the same problem as above will be encountered in the case where roadway tunnels or sheltered tunnels are to be constructed as a pollution control measure for existing roads.
The present invention relates to a method of efficiently adsorbing and removing NOx which is present in low concentrations in gases discharged by ventilation from highway tunnels.